Chapter 23

• Ecology, the Environment, and Us are important aspects of Biology

Earth as an Ecosystem

• Ecology studies interactions among organisms and their environment
• Energy comes from the sun
• Green plants capture solar energy and transfer it to organisms.
• Materials cycle between organisms and living / non-living components because there is no other source of new materials

Biosphere

• Biosphere: The part of Earth that supports life and consists of many ecosystems
• Population: Includes all individuals of the same species in an area
• Community: living species in an ecosystem that can potentially interact.
• Ecosystem: Organisms in a specific geographic area, together with their physical environment
• Niche: An organism's role in the ecosystem is determined by physical, chemical, and biological factors
• Habitat: A place where an organism lives, and is a part of the overall niche

Ecological Succession

• This is the sequence of changes in the species composition of a community over time
• Two types of succession are: Primary and Secondary

Primary Succession

• Occurs where no previous community existed and not even soil is present at the beginning
• Pioneer species: First living things, such as lichens, that invade an area to begin soil formation
• Climax community: Temperature, rainfall, nutrient availability, and exposure to sun and wind determine which kind of the climax community forms. This occurs after pioneer species

Secondary succession

• Occurs when an existing community is cleared by fire or volcanic eruption
• Soil is present at the start
• Initial invaders include grasses, weeds, and shrubs

Energy Flow

• Energy is supplied by the sun, which plants and algae trap and transform into glucose using photosynthesis
• Animals then eat the plants
• Photosynthesis uses the sun's energy to convert CO₂ and H₂O to carbohydrates, releasing O₂
• Trophic level: Feeding level between organisms
• Producers: Photosynthesizers like plants and algae, which start with CO₂ and form the lowest trophic level
• Consumers: Use energy stored by producers and form higher trophic levels

Energy Flow - Consumers By Food Source

• Herbivores: Consumers that eat only plants, noted as 1° consumers
• Carnivores: Consumers that feed on herbivores (2° consumers) or other carnivores, also known as meat eaters (3° consumers)
• Omnivores: Consumers that eat both plants (1°) and animals (2° and 3° consumers)
• Decomposers: Consume dead organic material for energy and release inorganic material for producers

Food Chains and Food Webs

• Food chain is a simplistic, linear sequence
• Food web represents more realistic patterns and includes many organisms that eat at several trophic levels

Energy Transfer

• Energy is lost when transferred from one trophic level to the next
• About 10% of energy available at one trophic level is transferred to the next
• Biomass, or the dry weight of an organism, is the only energy converted and available to the next higher trophic level

Biological Magnification

• Biological magnification is the concentration of nondegradable chemicals increases in organisms at successive trophic levels

World Hunger

• World hunger: Only about 10% of the energy captured by one trophic level is available to the next
• Less land would cultivated and more people could be fed if people adopted a vegetarian diet

Biogeochemical Cycles

• Earth's resources are limited and would be depleted without nature's recycling
• Materials move through transfers from living to nonliving systems and back again in recurring pathways

Water Cycle

• Water moves from the atmosphere to land as precipitation and returns via evaporation and plant transpiration
• Large amounts of water are temporarily stored in living things
• Human activities such as deforestation, altered runoff patterns, freshwater overuse, polar ice loss, and contamination disrupt the water cycle

Carbon Cycle

• Carbon moves from the environment into living things and back
• Living organisms need carbon to build molecules such as: Proteins, Carbohydrates, Fats and Nucleic acids
• Carbon dioxide (CO₂) is removed from the environment by producers during photosynthesis via sunlight
• Carbon in organic molecules then moves through the food web
• Carbon is returned to the atmosphere as CO₂ during cellular respiration
• Some carbon is sequestered in wood of trees, limestone, and fossils fuels
• Decomposition of dead plants and animals, erosion of limestone, and combustion release sequestered carbon
• Human activities increase CO₂ levels in the atmosphere through burning fossil fuels and deforestation
• Increased atmospheric CO₂ results in global warming and increased ocean acidity

Biodiversity

• Biodiversity refers to the species richness, including the number and abundance of species in a given area.
• Biodiversity is decreasing globally
• Habitat destruction and climate change are largely responsible for the decline
• Human disturbances lead to changes in biodiversity

Mass Extinctions

• Mass extinctions involve the loss of many species. These have occurred in the past, but never before due to human involvement
• Scientists estimate that species are currently being lost at a rate of 100 per day or more

Causes of Biodiversity Loss

• Habitat destruction is a cause
• The introduction of Alien species is a cause
• Overexploitation is a cause

Why Biodiversity Loss Matters

• Why should we care about the loss of biodiversity?
• Genetic diversity is useful to crossbreeding and genetic engineering
• Having only one variety of a plant predominates, changing conditions might completely wipe out that food source
• Plants may provide new drugs
• Organisms are critical to properly functioning biogeochemical cycles
• Since life is interrelated, losing one plant or animal may unexpectedly impact others